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Why LAH reductions can suck my phat dick!!!
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Author Topic: Why LAH reductions can suck my phat dick!!!
The Alchemist
Member posted 07-01-99 09:54 PM
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Ok, this is the last time I'm going to bug you guys and gals with my sorrows with LAH reductions of ß-nitropropenes but the following is an account of unbeleivable fuckin' bullshit that must be shared.
The Alchemist has given up the idea of creating MDA from piperonal for some time and has pursued other loves such as PCP derivatives (boy, are they great!!) cuz the LAH rxn just wasn't working out at the time. Now, since he hasn't touched the holy flask for a little while he decided go back to his roots and try out piperonal->MDß2nitropropene->MDA once again. The method used for nitropropene formation is that of Rhodium's cold base synth as found in TS II. Here it goes...
15g of piperonal was disolved in 40ml of MeOH and 7.1g of EtNO2 was added once all the piperonal had dissolved. This was placed in an ice/salt bath so that the temp of the soln could reach 0°C. When the temp reached 0°C, 4g freezing cold NaOH in 20ml dH2O was added drop wise and produced some white precipitate. This was stirred for another hour. Then, 100ml ice cold dH2O was added slowly and produced shitloads of white precipitate. This was then all added to 100ml of ice cold 2M HCl which turned beutiful colors and produced bright yellow crystals at the bottom of the flask (nitropropene). This was allowed to stir for a while in the ice bath and then the crystals were filtered in a Buchner funnel. These crystals were washed with some cold dH2O and sucked dry. These crystals were thrown into another flask and recrystallized from boiling IPA. It takes very little boiling IPA to dissolve the crystals so I'm wondering if this is a good recrystalization solvent. This was stuck in the freezer for 30 min and the yellow crystaline precipitate was filtered once again. This was allowed to air dry overnight and yeild was 11.4g MDß2nitropropene. (55% yield)
6.7g of LAH was suspended in 100ml of THF. (Note: Both the LAH and THF came straight from an unopened bottle) A solution of 6g nitropropene and THF was made. This soln was slowly added to the LAH/THF cuz the shit is extremely exothermic. Once all the shit was added, the soln was refluxed for 36 hrs (just like Shulgin sez). I did not notice any change in color of the LAH/THF suspension like Strike sez is supposed to happen. The excess hydride was destroyed w/ 7.2ml IPA followed by 7.2 ml 15% NaOH followed by 17ml dH2O. The LAH was converted into a bunch of white lithium and aluminum slats which was vacuum filtered. The THF was removed and some 2M HCl was added to the resulting clear/yellow (?!?!?) residue. The water then became a murky white with some of this clear oily shit st the bottom. But MDA is supposed to dissolve in HCL godammit!!!! This was then put through a standard A/B extraction which consisted of washing the HCl layer with DCM, basifying the water layer and extracting w/ DCM. when the DCM wasfinally evaporated it yeilded.........NOTHING!!!!
Holy shit I'm gonna put my fist through the fucki' wall.
Since the LAH was fresh out of the can and the THF was fresh out of the bottle, The ALchemist has to omit those as the problems. Even from a pre-opened bottle of THF (which was sittin around for 5 months) The Alchemist was able to form beutiful Grignards from which came some high quality dissociatives. Since the piperonbal DID react to form the nitropropene as stated my only thought is that the nitropropene crystals were impure. But how since thy were recrystallized?!?!?
No matter...next time the nitropropene will be turned into some ketone which can be worked with for fuck's sake!
Sorry about all the bullshit but you beez are the only people I can butch to about this shit.
until next time...
the alchemist
The Alchemist
Member posted 07-01-99 09:56 PM
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did I say "butch too???" silly me, I meant "bitch."
spitball
Administrator posted 07-01-99 10:38 PM
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Hmm..usually those both mean the same thing...
I think there's a word for that.
-spitball-
yellium
Member posted 07-02-99 02:55 AM
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Wierd. LAH reductions are supposed to be failsafe, as I've been told. Then again, I've seen the stuff in action this week for the first time, so I'm no expert. I guess your THF was still too wet. Was there a lot of bubbling when you added the THF? If so, better dry your THF. See Vogel for details. (BTW:in some labs, LAH is used as drying agent.)
But let me tell you a story about what my elves did last weekend, when they
tried to prepare 2cb.
(Oh, and before you comment on their lab technique: yeah, I know it sucks. Was the reason that they decided not to start a career as organic chemist. Does anybody know where you can get better elves? ACME? )
OK, read this, shiver and be warned. Don't make the mistakes they made.
One of the things they found out is that you should preferable use a lot of solvent. The problem was that they were a little limited on dry THF.
They noticed that shulgin & all used lots of THF; all they'd got was 250 ml for 13 grams of LAH and 26 grams of nitrostyrene. Poured 100 ml THF on 13 gr LAH, which gave a good amount of bubbling (damn! and they'd been drying this stuff for four days on Na!). They knew this is the wrong order of adding things, but the LAH was standing there from the previous weekend when they found out that their THF was *very* wet. Well, proved that the LAH was still OK.
Now, they don't know what magical
properties the nitrostyrene has in other labs, but it was impossible to dissolve in 150 ml THF at room temp. Damn again!
(BTW: anyone knows how much nitro compound you can dissolve in hot/cold THF?)
So, in zwit's spirit, with the LAH waiting for something to be reduced, they decided to just continue and boldly add their nitro-suspension. Well, they knew that things would be a little rough, but if you add four drops and see a little flame escaping, you know you're going to be late home tonight :-|
They soon found out that chilling the whole mess makes the addition less troublesome. O, and make sure you don't have any undissolved LAH on the walls of your flask. And don't give the fscking stirrer a chance to get
stuck!.
Adding the suspension is no fun: it tended to clog up the addition funnel. Using a pasteur pipette to carefully push the stuff through the hole in the crane without letting everything run suddenly into your flask is an adventure in itself.
After two hours of dripping & pushing things got a bit smoother. Addition didn't produce as much heat&smoke as before. Afraid that they would run out of active LAH, they stopped the addition here. After drying and weighing the the remaining nitro, they figured out they'd still added 15 grams of nitrostyrene.
From then on, everything went pretty smooth. Let the stuff reflux and see the color turn from grayish green to grayish brown to grayish purple/brown.
24h later:Workup was easy. Destroyed the LAH with IPA (keep your ice nearby!). Added NaOH. They didn't recall any spectacular fsckups over here. Proceeded to brominate the stuff. Went smooth ditto.
One thing about xtalizing 2cb: stick to the recipe Shulgin gives in PiHKAL. Impossible to fuck up, if you scale all numbers according to your estimated amount of 2cb. Gives you a nice solid chunk of crystals. There's only one thing `dangerous': wear gloves when you scrape the crystals out of your flask. They did, but for some fscking reason the work-up elve accidentally got a tiny bit of unwashed 2cb powder on her right finger *before* putting on gloves. Was only .5-2mg, but definately noticeable.
Great stuff, BTW. Think I prefer it over honey.
Bright Star
Member posted 07-02-99 11:03 AM
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Your LAH was not dry.
You can never take THF from the bottle and use it! Never! Never!!! THF is hygroscopic and will take water out of the air! All bee it, a very little water... but it will!!! And it will be plenty to ruin your reaction!!!
You must first dry some molecular sieves, a sealable bottle, and some Magnesium sulphate in the oven at 250C for several hours. Then, dump the MgSO4 in the THF ... shake and wait 20 minutes, shake again ... add more MgSO4, shake again .... wait an hour. Put a centimeter of molecular seves in the bottom of the sealable bottle, and pour the THF into it and seal with top+wax/parafilm untill needed.
Even anhydrous THF has water in it. Never take anything for granted! You will waste materials, money, and your time.
Yellium ... I like that stuff over honey, too ... So nice!
The Alchemist
Member posted 07-02-99 12:44 PM
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Then why could this same Fisher brand THF be used for preparing grignard reagents beutifully? This bottle used for the reduction was unopened. The grignard reaction was carried out in THF that came from an already opened bottle and grignard reactions are especially sensitive to water.
That ketone synth from nitropropene looks real good though. High yeilds, too.
Thanx for your help.
the alchemist
yellium
Member posted 07-02-99 03:53 PM
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As I've been told, grignards are a lot less water-sensitive than LAH reductions.
BTW, if this is your first LAH reduction, be prepared to get your *ss blown off. On *several* occasions during the above sketched attempt of adding the nitrostyrene they got a mini-explosion in their flask. If you use a super-saturated nitrostyrene solution, you'll end up with a lot of solid nitro building up on the side of your flask, and eventually lumps of it will fall in the LAH solution. Keeping a constant stream of N2 over it might have saved my elves career. And elves with good lab techniques have pretty long delivery times.
So use enough *dry* solvent and everything will probably be OK.
(BTW2, Vogel also says that you shouldn't put out LiAlH4 fires with a CO2-based fire extinguisher. Now that's useful information if you also have 500 ml of burning THF coming out of your fumehood..)
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